Resistance spot welding system



Nov. 25, 1941. HAMBERS 2,264,067

RESISTANCE SPOT WELDING SYSTEM Filed Aug. 19, 1939- 7mm APPL/CAT/MS 0FWELD/AC6 CURRE/WC H w //4 HOT/4770M 0F SHAFT /7 620556 83 I I i 'M] L-\SWITCHES /8/1ND l9 EfFORE 4 wan/Na OPERATION AND OPE/VS THESE SWITCHESInventor": Dudley E. Chamber's,

by WW4, His Attorney.

Patented Nov. 25, 1941 RESISTANCE SPOT WELDING SYSTEM Dudley E.Chambers, Scotia, N. Y., assignor to General Electric Company, acorporation of New York 7 Application August 19, 1939, Serial No.291,035

6 Claims.

My invention relates to an ampere second consistency control forresistance spot welding systems.

In the resistance spot welding of stress members or other importantproducts where it is not possible to make mechanical tests to determinethe dependability of the welds, I propose to determine theirdependability by comparing the ampere second value of each weld with theampere second value of a standard weld and to indicate undesirablevariations from the standard by suitable signals or by arresting theoperation of the welding system or both.

Since, in resistance spot welding, the welding pressure can beaccurately controlled and checked, and furthermore, since the thicknessand surface condition of the work parts are fairly uniform, the onlyvariation that may result in a defective weld is that due to variationsin the time and amount of current flowing. Thus, the ampere second valuefor each weld gives a dependable indication of the nature of the weld.

Variations in the amount and time of flow of the welding current mayresult from many causes. When the flow of welding current to successivespot welds is controlled by a mechanically operated switch, faultyoperation of the switch may vary both the time and amount of currentsupplied in making a weld and may result in a defective weld if thevariation from the desired normal is too great. Even in electric valvecircuit controls where the time and amount of welding current flowing isgoverned by a controlled rectifier, occasions arise when, due to thefaulty operation of a rectifier which has not yet failed, an incorrectamount of welding current is supplied in making a weld. Furthermore, inportable spot welding operations where extremely long leads are employedfor supa need in the resistance welding industry for a reliable meansfor indicating the consistency of welding operations that follow oneanother at a high rate of speed.

It is an object oi my invention to provide such means.

Further objects of my invention will become apparent from the embodimentthereof diagrammatically represented in the attached drawing.

In accordance with my invention, the ampere second value of the weldingcurrent, or as otherwise stated, the time integral of the weldingcurrent flow, is determined for each weld as a voltage charge on acondenser and a relay system is employed to compare this voltage at theend of each welding operation with a predetermined standard voltageequal to the voltage to which said condenser is charged by the amperesecond value of a standard weld and thereafter to discharge saidcondenser before the next welding operation. Consequently, my systemwill operate at speeds limited only by the operating time of the relaysystem.

In the drawing, the work to be welded is indicated at III betweenelectrodes II which are connected to the terminals of the secondary I!of a welding transformer IS. The primary ll of this transformer isconnected through a circuit controlling device IE to a source ofaltemating current supply IS. The circuit controlling device may be amechanical or electromechanical switch or an electric valve circuitcontrol such as described and claimed in United States Letters PatentNo. 1,935,413 to David C. Prince,

granted November 14, 1933, which functions to' supply timed applicationsof welding current to the welding electrodes.

The control illustrated may be associated with any spot welding machine,whether of the type in which the electrodes are moved into and out means[5.

of engagement with the work for each weldin operation, or of the typewhere the electrodes are rolled along the work while the welding currentis periodically supplied thereto. In either case, a shaft l1 forming apart of the machine or associated therewith is employed for closingcam-operated switches I8 and I! after the electrodes engage the work orbefore welding current is supplied thereto and for opening theseswitches a short time before the next welding operation.

The closure of switch [8 completes the initiating circuit 20 of thecircuit controlling means I5; starting the flow of welding current tothe electrodes H. The flow of welding current may be interrupted by theopening of this switch or by the operation of a timing means formingpart of or associated with the circuit controlling During each timedapplication of welding current, a condenser 2| is charged to a voltagevalue depending on the time integral of the welding current. Thiscondenser is charged through a full wave vacuum tube rectifier 22 of thehot cathode type which receives its input voltage from the tappedsecondary 23 of a voltage transformer '24 whose primary 25 is connectedacross an adjustable -resistance 26. This adjustable resistance isconnected across the secondary 21 of a current transformer whose primaryis connected in'the welding circuit between the circuit controllingmeans and the welding electrodes As illustrated in the drawing, theconnection is made in the primary circuit of the welding transformer. Aresistance 28 connected in circuit with the rectifier 22 and condenser2| determines the charging rate for the condenser. This resistance mayalso be made adjustable.

It was discovered that the electron emission of the cathode of rectifier22 generated a voltage which charged condenser 2| so that under certaincircumstances the voltage on the condenser would not give a truerepresentation of the ampere second value of the welding current flowingduring certain welding operations. As pointed out and claimed inthecopending application of Earl B. McDowell, Serial No. 291,025, filedconcurrently herewith and assigned to the same assignee as the presentinvention, the disturbing efiects of this self-generated voltage may beeliminatedbyapplying a bias voltage in circuit with rectifier 22 andcondenser 2|. This bias voltage may be obtained from a dual resistancecomprising sections 29 and 30 and sliding contacts 3| and 32 which areadjustable relative to'one another to give the desired value of biasvoltage and simultaneously adjusted along sections 29 and 38 to permitthe proper adjustment of the voltage obtained across resistance 38.Sections 29 and 30 of this resistance are of equal value and. areconnected in parallel with one another and in series with a resistance33 across a portion of a voltage divider forming part of a vacuum tubevoltmeter circuit This voltage divideris made up of series connectedresistances 34, 35, 36, 31 and 38. A sliding contact 39 is provided foradjusting the voltageapplied across resistances 29, 38 and 33.

A source of direct current voltage for the above-described voltagedivider is obtained from the source of supply 16 througha transformer48, a rectifier 4|, a filter circuit 42, and a resistance 43. A voltageregulator 44 is also connected across this'voltage divider. This voltageregulator comprises a glow discharge device which when in a conductivecondition maintains a substantial constant voltage'across its terminalsfor different values of current flowing therethrough.

An electric discharge device of ,the high vacuum type 45 is alsoconnected across this voltage divider through a circuit including amilliammeter 46 and 'a resistance 41. Discharge device 45 is providedwith a cathode 48, a control grid 49 and an anode 58. The cathode isheated by a filament 5| whose heating eflect is maintained constant bythe current supplied thereto through a circuit including a ballast lamp52 and a resistance 53 from a secondary winding of the transformer 48.The voltage drop across resistance 38 of the voltage divider betweenterminal 54 and sliding contact 55 places the con'-' trol grid at theproper negative potential relatlve to the cathode. This control grid isnormally maintained at ground potential through a resistor 56, oneterminal of which is connected to the ground connection 51.

The positions of sliders 32 and 39 on resistances 38 and 31 of thevacuum tube voltmeter places the positive charged terminal of condenser2| at some positive potential above ground. If the charge attained bycapacity 2| as the result of a welding operation is equal to thepotential difierence between ground and slider 32 no change in thepotential of control grid 49 of the electric discharge device 45 .willoccur when the negative terminal of condenser 2| is applied to thecontrol grid. However, if the charge on the capacity is either more orless than the potential determined by the adjustment of slider 32,control grid 49 of the electric discharge device 45 will be shifted awayfrom ground potential for an instant when the negative terminal of thecapacity is applied thereto. If the voltage across the capacity is toohigh, the control grid 49 becomes more negative and less current issupplied through the electric discharge device 45 and resistance 41resulting in a decreased voltage drop across resistance 41. On the otherhand, if the condenser charge is too low, the voltage drop acrossresistance 41 increases.

The resistance 41 is in the control circuit of electric valves 58 and 59and variations in voltage across resistance 41 controls the conductivityof these valves, and consequently, the operation of relays 68 and 6|.

Electric valves 58 and 59 are preferably electric discharge devicesofthe type employing an ionizable medium, such as a gas or vapor.Electric valve 58 is provided with an anode 62, a cathode 63, and a grid64, and electric valve 59 is provided with an anode 6.5, a cathode 66and a grid 61. The control circuit voltages between grid and cathode forelectric valve 58 includes the alternating current component of thesecondary winding 68 of a transformer 69, the voltage drops acrossresistances 41 and 34, andthat portion of resistance 35 included in thecircuit by sliding contact 18 in engagement therewith. The controlcircuit voltages between grid and cathode for electric valve 59 includesthe alternating cur-.

sistances 41 and 13 and that portion of resistance 14 included in thecircuit by sliding contact 15 in engagement therewith. The filaments 63and 66 of electric valves 58 and 59 are'supplied with heating current bysecondary windings of the transformers 69 and 12 and the load or outputcircuits of these valves including the operating windings 16 and 11 ofrelays 68 and 6| are energized by secondary windings 18 and 19 of thesesame transformers. The primaries 88 and 8| of these transformers areconnected to the source of supply l6. 7

Relay 60 controls through its contacts 82 the energization of a-signallamp 83 and the operating winding84 of a relay 85. Upon operation,

its holding circuit and maintains the illumination of lamp 89 throughits contacts 92 and opens its contacts 93 in the initiating circuit 20of the energizing circuit of the circuit controlling device I6. Lamps 93and 99 are extinguished and the relays 85 and 9| are returned to theirnormal positions by the momentary opening of the push-button switch 99located in the holding circuit for these devices.

The connection of condenser 2| with the vacuum tube voltmeter abovedescribed is controlled by relays 95 and 96. The comparison circuit iscompleted through contacts 91 of relay 96 and contacts 98 of relay 9.5.Before the next welding operation, condenser 2| is discharged through acircuit including contacts 91 of relay 96, contacts 99 of relay 95, anda resistor I00.

As described and claimed in the above referred to application of Earl B.McDowell, a resistance or impedance device IOI is connected acrosscondenser 2I in the control circuit including the switching means abovedescribed for connecting this condenser with the vacuum tube voltmeter.This impedance has a low value relative to the value of the leakageimpedance of this control circuit in order to prohibit undesiredvoltages building up across the condenser 2I due to leakage currents.

Any suitable timing circuit control may be employed for operating relays95 and 96 in timed sequence during a welding operation so long as relay96 operates to close its contacts 91 after welding current has ceased toflow and relay 95 closes its contacts 99 and opens its contacts 98 afterthe vacuum tube voltmeter has had an opportunity to function. Theseoperations may be secured by initiating through switch I9 the functionof two time delay circuits such as described and claimed in UnitedStates Letters Patent No. 2,171,347 of Elbert D. Schneider, August 29,1939, for Time delay relay, assigned to the same assignee as the presentinvention.

In the arrangement illustrated, the operating winding I02 of relay 96 iscompleted through switch I9 and electric valve I 03 and the operatingwinding I 04 of relay 95 is completed through switch I9 and electricvalve I05. These electric valves are preferably .electric dischargedevices of the high vacuum type.

Since the timing circuits embodying these electric valves are the sameonly the control for electric valve I03 will bedescribed.

In the timing circuit embodying electric valve I03, a capacity I06shunted by a high resistance I'I is charged by the flow of rectifiedcurrent between the grid I09 and the cathode I09 of electric valve I03so that the terminal connected to the grid becomese charged to anegative value. This occurs during negative half cycles of the source ofsupply I6 through the following circuit while switch I9 is open: fromone terminal of the source of supply I 6, through conductor IIO,resistance III, sliding contact II2 engaging this resistance, capacityI06, grid I09 and cathode I09 of valve I03, resistance H3 and conductorsIll and H5 to the other terminal of the source of supply I6. When theswitch I9 is closed, the connection of the cathode I09 of electric valveI03 is effectively transferred from conductor II5 to conductor I I0 anda circuit is provided through electric valve I03 for energizing windingI02 of relay 96. For a time determined by the discharge resistance I0'I,capacity I06 maintains the grid I08 of electric valve I 03 suflicientlynegative against the bias voltage across resistance II I forming part ofa voltage dividing circuit with resistance II6, to prevent currentflowing through electric valve I03 in quantities suflicient to operaterelay 36. After a predetermined time, the alternating current componentof voltage across resistance III becomes dominant andv cuit justdescribed obviously depends on various factors such as the value ofcapacity I06, the value of resistance I01, and the setting of slider II2on resistance III. The movement of this slider provides aconvenientmethod of varying the time interval in the manner described.

The timing circuits embodying electric valves I03 and I05 are set sothat beginning with the welding operation electric valve I03 energizeswinding I02 of relay 96. suiliciently to operate this relay a short timeafter welding current ceases to flow and electric valve I 05 energizeswinding I 05 of relay suiiiciently to operate this relay a short timethereafter so that between the operating periods of relays 93 and 95 thevacuum tube voltmeter circuit may function to compare. the charge oncondenser 2I with the predetermined voltage of the vacuum tube voltmetercircuit corresponding to the voltage to which the condenser is chargedin the making of a standard weld. The operation of relay 95 shouldfollow the operation of relay 96 before condenser 2| has dischargedthrough resistance 56 to a voltage value that would give a faultyoperation of the relay system controlled by the vacuum tube voltmeter.Before the next welding operation, switch I9 must have opened for asufiicient length of time to allow the capacitors of the timing circuitto become charged again ready for the next timing operation initiated bythe closing of switch I9.

In the drawing, the system has been illustrated in its deenergizedcondition. Normally, electric valve 58 is non-conducting and electricvalve 59 is conducting resulting in the indicating circuit beingdeenergized by reason of both relays 60 and 6| having their contacts 82and 98 open.

In view of the above description. the operation of the system isbelieved to be apparent. Briefly summarized, it is as follows: After theelectrodes II engage the work I0, switches I9 and I9 are closed. Theclosure of switch I3 initiates a timed application of welding currentwhich, through rectifier 22, charges condenser 2| to a voltagecorresponding to the ampere second value of the welding current. Theclosure of switch I9 initiates the operation of the timing circuitsembodying electric valves I03 and I05 which are so adjusted that afterthe welding current has ceased to flow, relay 96 closes its contacts 91.This completes the connection of condenser 2I with the vacuum tubevoltmeter. If the charge attained by the capacity as the result of aweld is equal to the potential difference between ground and the settingof the slider 32 on resistance 30, no change in the grid potential ofelectric valve 45 will result when the negative terminal of capacity 20is applied thereto because its grid is normally maintained at groundpotential through resistance 56. However, if the charge on capacity 2Iis either more or less than the potential determined by the adjustmentof slider 32 on resistance 30, the grid of electric valve 45 will beshifted away from ground potential for an instant when the negativeterminal of capacity 2I is applied thereto by the operation of relay 96.If the voltage across capacity 2| is too high, as pointed out above, thevoltage drop across resistance 41 decreases and electric Valve 39 isrendered non-conducting permitting relay 6| to close its contacts 88.The closure of these contacts will light lamp 89 and operate relay 9|which by closing its contacts 92 maintains its energization and theenergization of lamp 89 until switch 94 is momentarily opened to resetthe system. The operation of relay 9| also opens control circuit 20 bythe opening of its contacts 93. This will prohibit the initiation ofanother welding operation until the circuit is reset by operating pushbutton 94. On the other hand, if the voltage of condenser 2| is too low,the-voltage drop across resistance 41 will increase causing electricvalve 58 to become conductive and thus operate relay 60.- This relay, byclosing its contacts 82, lights lamp 83 and operates relay 85 which, byclosing its contacts 86, maintains its energization and the illuminationof lamp 83 and at the same time opens control circuit 20 of the circuitcontrolling device l through its contacts 81. This prevents furtheroperation of the welding system until the reset button 94 is momentarilyopened to deenergize relay 85. It is thus apparent that after eachwelding operation the system functions to indicate whether the amperesecond value of the weld just made is too high or too low. 0n the otherhand, if the ampere second value is correct, no indication will be givenand the system will be free to continue its operation.

A short time after the vacuum tube voltmeter and the relay systemassociated therewith have had an opportunity to function, the timingcircuit embodying electric valve I05 operates, energizing the relay 95.This relay disconnects capacit-y 2| from the vacuum tube voltmeter atits contacts 98 and through its contacts 99 completes a dischargingcircuit through resistance I00 for condenser 2|. Subsequently switchesl8 and I9 open. The time during which switch l9 remains open before thenext welding operation must be suflicient to allow the capacities inthetiming circuits including electric valves I03 and I05 to become chargedagain ready for the next timing operation initiated by the closing ofswitch l9.

In order to calibrate the system, standard welds having the properampere second values are made and the system adjusted by adjustingresistance 26 until the pointer on milliammeter 46 does not move, or atmost only slightly flickers when a weld is checked. The sensitivity ofthe indicator may be controlled by adjusting slider 32 on resistance andby adjusting sliders Ill and 15 on resistances 35 and 14 which latterare normally used to balance the low and high sensitivities but may beused to obtain additional sensitivity if the adjustment of slider 32 onresistance 30 is not suflicient. In the particular arrangement, it isusually advisable to adjust slider 15 because in doing so, it has noeffect on the voltage adjustment obtained by moving slider 10. The timedelay in the operation of relay 96 may be controlled by adjusting sliderH2 on resistance HI and the same adjustment may be made for relay 95inthe timing control associated therewith.

In order to simplify the diagrammatic illustration of the systemillustrated in the drawing, the usually employed time delay relay systemcontrolling the application of power to the anode circuits of the valveshas been omitted. The drawing has also been simplified by omittingmechanical features 01' the weldin machine embodying or havingassociated ther with the shaft l1, These and other simplifications havebeen made in order to present the invention as clearly as possible.

It is to be understood that various modifications may be made in thesystem illustrated and described without departing from the spirit andscope of my invention. I aim, consequently, in the appended claims tocover all those modifications which come within the true spirit andscope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a control system, a circuit, means for supplying a timedapplication of current through said circuit, means for determining as avoltage across a condenser the time integral of said application ofcurrent, means for establishing a standard voltage equal to the voltageto which said condenser is charged by the time integral of a desiredstandard application of current through said circuit, and means forcomparing the voltage of said condenser with saidstandard voltage aftersaid supply means has furnished a timed application of current throughsaid circuit.

2. In a control system, a circuit, means for supplying timedapplications of currentthrough said circuit, means for determining as avoltage across a condenser the time integral of each of said timedapplications of current, means for establishing a standard voltage equalto the voltage to which said condenser is charged by the time integralof a desired standard application of current through said circuit, meansfor comparing the voltage of said condenser with said standard voltageafter each timed application of current through said circuit, and meanshaving a predetermined time sequence relative to the time of saidcurrent applications and the time between them for connecting andcomparing said condenser voltage with said standard voltage and forthereafter discharging said condenser before another timed applicationof current passes through said circuit.

3. In a control system, a circuit, means for supplying timedapplications of current through said circuit, a condenser, means forcharging said condenser to voltage values, corresponding to the amperesecond values of successive timed appliacations of current flow throughsaid circuit, mean for establishing a comparison voltage equal in valueto the voltage to which said condenser is charged'upon the flow of adesired timed application of current through said circuit, and meansfor-comparing the voltage of said condenser with said standard voltageafter each application of current through said circuit.

4. In a control system, a circuit, means for supplying timedapplications of current through said circuit, a condenser, means forcharging said condenser to voltage values corresponding to the amperesecond values of successive timed applications of current through saidcircuit,

means for establishing a comparison voltage equal in value to thevoltage to which said condenser is charged upon the flow of a desiredtimed application of current through said circuit, means for comparingthe voltage of said-condenser with said comparison voltage after eachtimed application of currentandthereaiter discharging said condenser, asignal device, and means controlled in response to a predetermineddifference in said voltages for operating said signal device.

5. In a control system, a circuit, means for supplying timedapplications of current through said circuit, a condenser, means forcharging said condener to voltage values corresponding to the amperesecond values of successive timed applications of current through saidcircuit, means for establishing a comparison voltage equal in value tothe voltage to which said condenser is charged upon the flow of adesired timed application of current through said circuit, means forcomparing the voltage of said condenser with said comparison voltageafter each timed application of current through said circuit, and meansresponsive to a predetermined difierence in said voltages forautomatically arresting the operation of said means for supplying timedapplications of current through said circuit.-

6. In a control system, a circuit, means for supplying timedapplications of current through said circuit, a current transformerhaving its primary in said circuit and its secondary connected across aresistance, a condenser, a transformer having its primary connectedacross said resistance and its secondary connected through a resistanceand a rectifier in circuit with said condenser, means for establishing astandard adjustable voltage, means including a vacuum tube voltmeter forcomparing the voltage of said condenser after each timed application ofcurrent through said circuit with said standard voltage and forthereafter discharging said condenser before another timed applicationof current through said circuit, means controlled by said vacuum tubevoltmeter in response to a predetermined variation between the voltageof said condenser and said standard voltage for arresting the operationof said means for supplying timed applications of current through saidcircuit, and manually operated means for restoring the operation of saidmeans for supplying timed applications of current through said circuit.

DUDLEY E. CHAMBERS.

